1. Field
Various communication systems may benefit from mobility state estimation (MSE) enhancement. For example, communication systems that include small cell and heterogeneous network (HetNet) deployments may experience improved mobile performance of user equipment.
2. Description of the Related Art
With the development of mobile communication technology, there is an increased demand in high quality and high data speed of the connection that a User Equipment (UE) should be experiencing even at high speeds. For Long Term Evolution (LTE), the requirements of the speed may reach over 300 km/hr. In order to enable the UE to have a sustainable call and/or uninterrupted data connection while moving, the network may need to achieve large-scale coverage. The UE may need to complete several mobility processes, including cell selection and cell reselection in the IDLE state, and cell change in the RRC-CONNECTED state. In the mobility process UE is configured to have some network parameters. In order to get the optimal mobility performances when UE is under different speeds in the network, the configuration of these parameters may need to be adjusted accordingly. However, it has been identified that the current MSE mechanism may not perform well in heterogeneous network (HetNet) deployments or scenarios. A HetNet may be described as a radio access network that comprises layers of different-sized cells ranging from big (macrocells) to small (picocells and femtocells). However, it should be noted that in some areas the network may consist of similar type only (e.g., macrocells).
The concept of a HetNet has emerged in the context of Long Term Evolution (LTE) and LTE-Advanced. In order to reach the full bandwidth capacity of either technology, operators may need to supplement their traditional large macrocells with smaller cells, e.g., for providing additional capacity at usage hotspots.
HetNet may define how all those different-sized cells will work together, how hand-off among them will be achieved, and how interference among them will be minimized.
Therefore, if in the case of having HetNet deployment, the network may get the mobility state of UE, it may greatly improve the UE mobility performances. In Universal Mobile Telecommunication Systems (UMTS), so as to achieve the purpose and optimize the mobility performances, the mobility state is divided into 2 states. One is the normal-mobility state and the other is the high-mobility state. Further, in the LTE system, due to the support to the high speed scenario, the mobility state is divided into 3 states, including normal-mobility state, medium mobility state and high-mobility state.
When developing into the LTE-A system, in order to increase the coverage rate of high speed data, temporary network coverage and cell edge throughput, the Heterogeneous Network (HetNet) is introduced with a mix deployment of macro and low power nodes (LPN), which consist of picocells, H-eNBs (Home eNode B), LTE femtocells, and/or relay nodes.
In a heterogeneous network macrocells are regarded as the initial deployment, and picocells, H-eNBs and/or relay nodes are added for incremental capacity growth, richer user experience and in-building coverage.
In the UMTS system and LTE system, a relatively accurate UE mobility state estimation (MSE) is easy to achieve through the existing MSE algorithm. However, the existing MSE algorithm may not be suitable in the HetNet of a LTE/LTE-A system.
This is because all cell changes are conventionally counted equally in existing MSE, regardless of the cell size or duration. Therefore, a user equipment (UE) moving in a macrocell network counts cell changes, for example, cell reselections in IDLE mode, within the evaluation window and arrives to a certain MSE. Thus, if picocells are deployed in addition to a macro network, the density of the picocells greatly affects the MSE because of the relatively small size of the picocells.
In addition to this, there are short cell changes, for example, UE stays in a cell for short time before another cell change caused mainly by variations and uncertainty in cell change measurements as well as the irregularity of the cell borders. Ping-pong cell changes, where the UE goes from cell A to cell B and back to cell A again are removed from the traditional MSE according to the current 3GPP TS 36.304 V11.2.0 (2012-12) specification, herein incorporated by reference. However, any short cell change is a less robust indication for the macro-scale mobility. So, there are these two main aspects to deal with in order to provide a more robust indication for UE mobility aspect. For example, cell changes macro1→macro2→macro3 within a short time (so that UE could not have possibly moved through, e.g., a 500 meter macrocell, or even through a large portion of it) is likely a case of UE at border of 3 cells so that UE goes basically from macro1 to macro3, but makes a brief cell change to macro2 in-between. This is not a ping-pong as such and may be counted in a traditional MSE, but nevertheless it is a cell change that may be considered to introduce noise to the MSE, not so much real information on mobility state, especially on macro-scale.
Moreover, the traditional MSE does not count the ping-pong reselections/cell changes. In other words, the UE shall not count consecutive reselections between the same two cells into mobility state detection criteria if the same cell is reselected just after one other reselection.
This means that traditional MSE filters out ping-pong cell changes. In other words, cell 1→cell 2→cell 1 is not counted, or is counted as just one cell change instead of two. This may be useful in a HetNet scenario, where the effect of cell changes to picocells that are deployed sparsely in macro cells may be filtered out from MSE. However, this does not filter out all short cell changes. For example, short cell changes may have a significant impact on the MSE and mobility state, regardless of whether or not they are due to ping-pongs or involve small cells. Moreover, these short cell changes may not represent a true picture of the UE mobility.